Wavefront aberration measuring apparatus

ABSTRACT

A wavefront aberration measuring apparatus comprising: an illumination optical system provided to an incident side of a test lens; and a measuring optical system provided to an exit side of the test lens, the illumination optical system including an aperture stop capable of being opened and closed, and the illumination optical system being movable along an optical axis of the illumination optical system so as to adjust positions of the aperture stop and an entrance pupil of the test lens to have an optically conjugate relation with each other. Accordingly, it becomes possible to provide a wavefront aberration measuring apparatus capable of suppressing errors in measured result.

TECHNICAL FIELD

The present invention relates to a wavefront aberration measuringapparatus used for measuring wavefront aberration of a lens to bemeasured.

BACKGROUND ART

There has been known a Shack-Hartmann sensor as a method for measuringwavefront aberration. For example, there is an explanation as arepresentative case of a wavefront measuring sensor in Tsuruta, Tadao,Pencil of Rays Vol. 4, Singijutsu Communications, 1997, p. 212.

In an optical system of a wavefront aberration measuring apparatus formeasuring wavefront aberration generated in a test lens, an illuminationoptical system that illuminates the test lens with a bundle of rays anda measuring optical system that measures wavefront aberration of thebundle of rays are generally used.

In the measuring optical system, upon analyzing wavefront aberrationgenerated by the test lens, a shape of a projected aperture has to beknown. Accordingly, an aperture stop of the test lens is projected to bemeasured the shape thereof. In this instance, in order to derive thecenter of the aperture stop, the shape and the position of the aperturestop may be measured with fully stopping down the aperture stop.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, upon operating the aperture stop in the test lens to fully stopdown, the center of gravity of the test lens is shifted or an effect ofdeformation of the lens portion is generated upon driving the aperturestop, so that there is a possibility that errors are generated inmeasured result of the shape and the position of the projected aperturestop. As a result, there is a possibility that errors may be generatedin the measured result of wavefront aberration.

The present invention is made in view of the above-mentioned problems,and has an object to provide a wavefront aberration measuring apparatuscapable of suppressing errors in the measured result.

Way to Solve the Problems

According to a first aspect of the present invention, there is provideda wavefront aberration measuring apparatus comprising: an illuminationoptical system provided to an incident side of a test lens; and ameasuring optical system provided to an exit side of the test lens, theillumination optical system including an aperture stop capable of beingopened and closed, and the illumination optical system being movablealong an optical axis of the illumination optical system so as to adjustpositions of the aperture stop and an entrance pupil of the test lens tohave an optically conjugate relation with each other.

According to a second aspect of the present invention, there is provideda wavefront aberration measuring apparatus comprising: an illuminationoptical system provided to an incident side of a test lens; and ameasuring optical system provided to an exit side of the test lens, theillumination optical system including an aperture stop capable of beingopened and closed, and the measuring optical system and the test lensbeing movable along an optical axis of the test lens so as to adjustpositions of the aperture stop and an entrance pupil of the test lens tohave an optically conjugate relation with each other.

According to a third aspect of the present invention, there is provideda method for manufacturing a lens system having a plurality of lenscomponents, the method comprising steps of: assembling the lens systemwith disposing the plurality of lens components into a lens barrel;measuring wavefront aberration of the assembled lens system by means ofthe wavefront aberration measuring apparatus according to the firstaspect; and judging whether the lens system is good or not from themeasured result.

Effect of the Present Invention

The present invention makes it possible to provide a wavefrontaberration measuring apparatus capable of suppressing errors in measuredresult.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are drawings showing a wavefront aberration measuringapparatus according to an embodiment of the present invention, in whichFIG. 1A shows a state before adjusting to an optically conjugaterelation, and FIG. 1B shows a state after adjusting to the opticallyconjugate relation.

FIGS. 2A and 2B are views showing in detail of the adjustment shown inFIGS. 1A and 1B, in which FIG. 2A shows a state before adjusting to anoptically conjugate relation, and FIG. 2B shows a state after theadjustment.

FIGS. 3A and 3B are drawings showing a wavefront aberration measuringapparatus according to another embodiment of the present invention, inwhich FIG. 3A shows a state before adjusting to an optically conjugaterelation, and FIG. 3B shows a state after adjusting to the opticallyconjugate relation.

FIG. 4 is an enlarged view showing the test lens 3 shown in FIGS. 3A and3B.

FIG. 5 is a flowchart explaining an outline of a method formanufacturing a lens system according to the present invention.

MODES FOR CARRYING OUT THE INVENTION

Then, a wavefront aberration measuring apparatus is further explained indetail with reference to drawings according to an embodiment of thepresent invention. Incidentally, mechanical and electrical drawings withrespect to driving portions are omitted as a matter of convenience.Moreover, a portion having the same function is attached the samereference number, and duplicated explanations are omitted.

FIGS. 1A and 1B show a wavefront aberration measuring apparatus 1according to an embodiment. The wavefront aberration measuring apparatus1 is composed of an illumination optical system 10 and a measuringoptical system 20. A test lens 3 to be measured is disposed between theillumination optical system 10 and the measuring optical system 20, andwavefront aberration of the test lens 3 is measured.

The illumination optical system 10 is composed of a light source 12guided by an optical fiber 11, a lens 13, a filter 14, an aperture stop15, a lens 16, a stop 17, and a projection lens 18, and disposedlinearly to an incident side of the test lens 3. The illuminationoptical system 10 is movable along an optical axis A. Moreover, theprojection lens 18 is movable along the optical axis A. The aperturestop 15 is provided vertically to the optical axis A, and able to beopened and closed. The diameter of the aperture stop 15 can be setarbitrary.

The stop 17 is disposed to a front focal point of the projection lens18. A rear focal point of the projection lens 18 coincides with anentrance pupil of the test lens 3. Moreover, the aperture stop 15 isdisposed to a front focal point of the lens 16. The stop 17 is disposedto a rear focal point of the lens 16. Furthermore, the aperture stop 15is disposed to a rear focal Point of the lens 13. Accordingly, theaperture stop 15 and the entrance pupil of the test lens 3 become anoptically conjugate relation, so that an image (a virtual image) of thestop 17 is formed on a position of an image plane stop 21 describedlater by the test lens 3. Incidentally, the entrance pupil of the testlens 3 comes to a position where an aperture stop 35 of the test lens 3is optically projected. Moreover, the aperture stop 35 of the test lens3 is remained open.

The measuring optical system 20 is composed of the image plane stop 21,an objective lens 22, a first relay lens 23, a filter stop 24, a secondrelay lens 25, a Shack-Hartmann wavefront sensor 26, a change mirror 27,and an imaging device 28, and these components are disposed linearly toan exit side of the test lens 3.

The wavefront sensor 26 is composed of a multi-lens array 26 a and animaging device 26 b. The multi-lens array 26 a is constructed byarranging a large number of lens elements (not shown) adjoiningtwo-dimensionally. Each minute aperture (not shown) of each lens elementis disposed perpendicularly to the optical axis A. Each minute apertureof each lens element has positive refractive power, and is formed with,for example, a quadrilateral whose outer circumference has four sides. Asectional view of the lens element parallel to the optical axis has aconvex shape projecting on only the incident surface side over entiresurface of the minute aperture, and the outer circumference of the lenselement is formed by curved lines. One pair of opposite sides of theouter circumference is composed of a convex arc toward outside and aconcave arc toward inside, and the other pair of opposite sides of theouter circumference is composed of a convex arc toward outside and aconcave arc toward inside. In this manner, the multi-lens array 26 a isconstructed by arranging a large number of lens elements having the sameshape adjoining two-dimensionally, so that each element adjoins with nogap. The imaging device 26 b is constructed by charge coupled devices(CCD), and is disposed on the focal point of the multi-lens array 26 a.

Since the optical path can be changed by a right angle by means of thechange mirror 27, the multi-lens array 26 a and the imaging device 28are optically conjugate positions. The filter stop 24 suitably limitsfrequency of the bundle of rays.

As shown in detail in FIG. 4, the test lens 3 is constructed by a lensgroup composed of a number of lenses 31, 32, 33, and 34, and includes anaperture stop 35. In FIG. 4, A denotes a principal ray of the incidentlight, B denotes the optical axis of the lens group composed of lenses31 through 34, 3 a denotes the center of the entrance pupil of the testlens 3, 3 b denotes the center of an exit pupil of the test lens 3, and35 a denotes the center of the aperture stop.

In the illumination optical system 10, light wave La of the bundle ofrays is collimated by the lens 13, adjusted the dimension of theaperture by the aperture stop 15, converged by the lens 16, andilluminates the stop 17. The light wave La illuminating the stop 17 isincident on the test lens 3 through the projection lens 18, and forms animage of the stop 17 on the position of the image plane stop 21. Thelight wave Lb incident on the measuring optical system 20 is collimatedto the parallel rays by the objective lens 22, expanded by the firstrelay lens 23 and the second relay lens 25, and projected on thewavefront sensor 26. An intermediate image plane is formed between thefirst relay lens 23 and the second relay lens 25, but the frequency ofthe bundle of rays is suitably limited by the filter stop 24.

In the wavefront sensor 26, the light wave is dividedly converged by themulti-lens array 26 a. Each of the dividedly converged light wave Lb isformed an image at a position corresponding to wavefront aberration, andeach imaged position M of the multi-lens array 26 a is measured by theimaging device 26 b. The measured data is stored in a data memory (notshown), analyzed by an analyzer (not shown), and displayed on a display(not shown).

Incidentally, the aperture stop 15 shown in FIG. 1A is not in a positionwhere the aperture stop 35 of the test lens 3 is optically conjugatewith. As a result, after passing through the test lens 3, the light waveLa is incident on the measuring optical system 20 with includingwavefront aberrations generated by the projection lens 18 and the testlens 3. Accordingly, the imaged position measured by the imaging device26 b is shown by wavefront aberration M′ shifted from an ideal wavefrontM0. However, the shift amount does not precisely show wavefrontaberration of the test lens 3.

In order to correct the above-described shift amount, the position ofthe projected stop 17 has to be adjusted to the center of the exit pupilof the projection lens 18. FIG. 2 shows this adjustment in detail. Asshown in FIG. 2A, after determining the projection position with movingthe projection lens 18 along the optical axis A, the whole of theillumination optical system 10 is moved along the optical axis A suchthat the exit pupil E of the projection lens 18 comes to the entrancepupil 35 of the test lens 3 as shown in FIG. 2B. In this instance, thewhole of the illumination optical system 10 may be move in a directionperpendicular to the optical axis A when necessary. Accordingly, theaperture stop 15 can be adjusted to the position optically conjugatewith the test lens 3. This state is shown in FIGS. 1B and 2B. In thiscase, the imaged position M of the light wave Lb passed through the testlens 3 coincides with the ideal wavefront M0. Accordingly, wavefrontaberration generated to the light wave La incident on the test lens 3along the optical axis A can be measured. Incidentally, in FIG. 1B, Cdenotes the outer most bundle of rays limited by the aperture stop 15.

In order to precisely detect the center M of the bundle of rays of thelight wave Lb, the aperture stop 15 is stopped down. Then, the image ofthe aperture stop 15 is imaged by the imaging device 28 so as toprecisely grasp the shape and the position thereof. Accordingly, thecenter M of the bundle of rays can be precisely obtained withoutstopping down the aperture stop 35 of the test lens 3. As a result,wavefront aberration can be measured with suppressing errors in themeasured result.

FIGS. 3A and 3B are drawings showing a wavefront aberration measuringapparatus 1 according to another embodiment, in which a case wherewavefront aberration of a bundle of rays incident on the test lens 3 ina direction inclined with respect to the optical axis B of the test lens3 is measured is shown. In this case, since the measuring optical system20 is disposed with inclining with respect to the optical axis A, thecenter 3 a of the entrance pupil of the test lens 3, which is anintersection of the optical axis A of the illumination optical system 10and the optical axis B of the test lens 3, and the center 3 b of theexit pupil of the test lens 3 are shifted in the optical axis Bdirection of the test lens 3, as shown in FIG. 4. The others are thesame as the embodiment shown in FIG. 1, so that explanations areomitted. Incidentally, in FIG. 3A, D denotes the center of the bundle ofrays proceeding to the entrance pupil of the test lens 3.

The wavefront aberration measuring apparatus is not limited to theabove-described embodiment. For example, a component capable of movingmay be the measuring optical system 20 instead of the illuminationoptical system 10. In this case, the illumination optical system 10 isfixed, and only the aperture stop 15 can be opened and closed. Themeasuring optical system 20 is movable along the optical axis B, and incooperation with the aperture stop 15 capable of being opened andclosed, the aperture stop 15 and the entrance pupil of the test lens 3are adjusted to the positions optically conjugate with each other. Inthis case, the wavefront sensor 26 is further made movable along theoptical axis B, so that the aperture stop 15 and the entrance pupil ofthe test lens 3 can be adjusted to the positions optically conjugatewith each other.

Moreover, it is conceivable that the wavefront sensor 26 of themeasuring optical system 20 is made movable along the optical axis Bwith respect to the fixed illumination optical system 10 in cooperationwith the aperture stop 15 capable of being opened and closed, so thatthe aperture stop 15 and the entrance pupil of the test lens 3 may beadjusted to optically conjugate positions. In this case also, theillumination optical system 10 may further be made movable along theoptical axis A, so that the aperture stop 15 and the entrance pupil ofthe test lens 3 may be adjusted to the positions optically conjugatewith each other.

Moreover, both of the whole or a portion (in particular, the projectionlens 18) of the illumination optical system 10, and the whole or aportion (in particular, the wavefront sensor 26) of the measuringoptical system 20 are made movable, so that the aperture stop 15 and theentrance pupil of the test lens 3 may be adjusted to optically conjugatepositions. In this case, the shape and the position of the entrancepupil can be further precisely measured.

In this manner, the present embodiment makes it possible to measureprecise shape and position of the exit pupil of the test lens withoutmoving the aperture stop of the test lens.

Moreover, in a lens for a recent electrified camera, although anelectrical movement is necessary to open or close an aperture stop, thepresent embodiment can omit an external connection and electric circuitfor driving.

Moreover, with opening and closing the aperture stop of the illuminationoptical system and with moving the whole or a portion of theillumination optical system or the whole or a portion of the measuringoptical system along the optical axis, it becomes possible to measurethe shape and the position of the exit pupil of the test lens.

Moreover, since the aperture stop of the test lens is not necessary tobe opened and closed, the measurement becomes further accurate withfewer error factors.

Accordingly, precise shape and position of the exit pupil of the testlens can be measured.

A shape of the lens element composing the multi-lens array 26 a isarbitrary. As for an imaging device, other than CCD, an image pickuptube and a complementary metal oxide silicon (CMOS) can be conceivable.

An outline of a method for manufacturing a lens system having aplurality of lens components is explained below with reference to FIG.5.

At first, the lens system is assembled with disposing a plurality oflens components into a lens barrel. Wavefront aberration of theassembled lens system is measured by means of the wavefront aberrationmeasuring apparatus shown in FIGS. 1A and 1B. Whether the assembled lenssystem is good or not is judged from the measured result.

The wavefront aberration measuring apparatus according to the presentinvention can be used for measuring a general optical apparatus such asan objective lens for a telescope, a camera and a microscope.

What is claimed is:
 1. A wavefront aberration measuring apparatuscomprising: an illumination optical system provided to an incident sideof a test lens; and a measuring optical system provided to an exit sideof the test lens, the illumination optical system including an aperturestop capable of being opened and closed and a projection lens, and themeasuring optical system and the test lens being movable along anoptical axis of the test lens so as to adjust positions of the aperturestop and an entrance pupil of the test lens to have an opticallyconjugate relation with each other.
 2. The wavefront aberrationmeasuring apparatus according to claim 1, wherein the measuring opticalsystem includes a wavefront sensor that is movable along the opticalaxis of the test lens.
 3. A wavefront aberration measuring apparatuscomprising: an illumination optical system provided to an incident sideof a test lens; and a measuring optical system provided to an exit sideof the test lens, the illumination optical system including an aperturestop capable of being opened and closed and a projection lens, and themeasuring optical system including a wavefront sensor that is movablealong an optical axis of the test lens such that the aperture stop andan entrance pupil of the test lens are adjusted to positions to haveoptically conjugate relation with each other.
 4. The wavefrontaberration measuring apparatus according to claim 3, wherein themeasuring optical system is movable along the optical axis of the testlens.
 5. The wavefront aberration measuring apparatus according to claim1, further comprising: an imaging device being disposed on an opticallyconjugate position with respect to the aperture stop and the entrancepupil of the test lens.
 6. The wavefront aberration measuring apparatusaccording to claim 1, further comprising: a lens array being disposed onan optically conjugate position with respect to the aperture stop and anentrance pupil of the test lens.
 7. The wavefront aberration measuringapparatus according to claim 1, wherein the measuring optical system isdisposed linearly with respect to the illumination optical system. 8.The wavefront aberration measuring apparatus according to claim 1,wherein the measuring optical system is disposed with inclining withrespect to the illumination optical system.
 9. A method formanufacturing a lens system having a plurality of lens components, themethod comprising steps of: assembling the lens system with disposingthe plurality of lens components into a lens barrel; measuring wavefrontaberration of the assembled lens system by means of a wavefrontaberration measuring apparatus; and judging whether the lens system isgood or not from the measured result, wherein the wavefront aberrationmeasuring apparatus comprises: an illumination optical system providedto an incident side of the lens system; and a measuring optical systemprovided to an exit side of the lens system, the illumination opticalsystem including an aperture stop capable of being opened and closed anda projection lens, and the illumination optical system being movablealong an optical axis of the illumination optical system so as to adjustpositions of the aperture stop and an entrance pupil of the lens systemto have an optically conjugate relation with each other.
 10. A methodfor manufacturing a lens system having a plurality of lens components,the method comprising steps of: assembling the lens system withdisposing the plurality of lens components into a lens barrel; measuringwavefront aberration of the assembled lens system by means of awavefront aberration measuring apparatus; and judging whether the lenssystem is good or not from the measured result, wherein the wavefrontaberration measuring apparatus comprises: an illumination optical systemprovided to an incident side of a test lens; and a measuring opticalsystem provided to an exit side of the test lens, the illuminationoptical system including an aperture stop capable of being opened andclosed and a projection lens, and the measuring optical system and thetest lens being movable along an optical axis of the test lens so as toadjust positions of the aperture stop and an entrance pupil of the testlens to have an optically conjugate relation with each other.
 11. Amethod for manufacturing a lens system having a plurality of lenscomponents, the method comprising steps of: assembling the lens systemwith disposing the plurality of lens components into a lens barrel;measuring wavefront aberration of the assembled lens system by means ofa wavefront aberration measuring apparatus; and judging whether the lenssystem is good or not from the measured result, wherein the wavefrontaberration measuring apparatus comprises: an illumination optical systemprovided to an incident side of a test lens; and a measuring opticalsystem provided to an exit side of the test lens, the illuminationoptical system including an aperture stop capable of being opened andclosed and a projection lens, and the measuring optical system includinga wavefront sensor that is movable along an optical axis of the testlens such that the aperture stop and an entrance pupil of the test lensare adjusted to positions to have optically conjugate relation with eachother.